The way that's being asked is confusing me a bit, so I'm not sure how to answer. It probably comes down to one of the following, though:
1. Normally, in order for a challenge to be initiated, the attacking player must complete a 2-step process of a) naming the challenge type and defending player, and b) declaring attacking characters. There is no room for player actions until the entire process of initiating the challenge is over. With Dragon Sight, the 2-step process is extended to a 3-step process of a) the attacking player naming the challenge type and defending player, b) the defending player declaring defending characters, and c) the attacking player declaring attacking characters. There still cannot break up process for initiating the challenge and there is no room for player actions until the entire (extended) process of initiating the challenge is over. So no, there are no player actions before declaring attackers or defenders with Dragon Sight, just like there are no player actions between announcing the challenge type/opponent and declaring attackers under normal circumstances.
2. The player action window between declaring attackers and defenders is an entirely separate and independent thing. It is not associated with declaring either attackers or defenders. So when Dragon Sight moves the declaration of defenders to before the declaration of attackers, there is no reason to think that it also moves the entirely separate and independent player action window, too. The action window after declaring attackers stays where it is. It does not disappear. It's just that there is no "declare defenders" on the other end of it. But it is still there if you want to do tricky things like use Lost Oasis to give an attacker stealth, then assign stealth no to keep a defender out of the challenge (those have already been declared), but to create the "after a character is stealthed" response opportunity.
The TL/DR version is that, as outlined above, only the framework event "declare defenders" is moved by Dragon Sight. Everything else stays the same - and you cannot interrupt the "initiate challenge" framework window (which now includes declaring defenders) with player actions.